On expressway and pushed on accelerator . . . . engine revved as if transmission was not in gear. I shifted over to “manual” and engine again engaged. Short time after, moved shifter back to “auto” side and engine performed as normal. 2000 / 4.0 engine - This is the second time this has happened. Electronic . . . . failing trans mission??? No warning codes or engine light etc.
Check the 2 bolts on the side of the transmission, these can come loose over time and may account for the symptoms you describe.
Always go simple first.